Many factors, including environmental responsibility efforts and modern environmental regulations on engine exhaust emissions, have reduced the allowable acceptable levels of certain pollutants that enter the atmosphere following the combustion of fossil fuels. Increasingly, more stringent emission standards may require greater control over either or both the combustion of fuel and post combustion treatment of the exhaust. For example, the allowable levels of nitrogen oxides (NOx) and particulate matter have been greatly reduced over the last several years. To address, among other issues, environmental concerns, many diesel engines now have a diesel oxidation catalyst (DOC) as well as a diesel particulate filter (DPF) within an exhaust system of the diesel engine purposed to reduce the amount of NOx and particulate matter released into the atmosphere.
In some diesel engine operating conditions it may be beneficial to provide hydrocarbons, typically in the form of diesel fuel, directly to the exhaust system of the engine at a location upstream of the DOC such that the hydrocarbons will react with the DOC to produce heat and raise temperatures within the DPF to a point sufficient to allow regeneration of the DPF. Unfortunately, hydrocarbons do not always react as desired with the DOC, and sometimes hydrocarbons slip through the DOC and enter the DPF where they may combust and result in unintended heat release and exhaust gas creation, a condition referred to as “hydrocarbon slip.”. The unintended exhaust gas creation often is visible as white exhaust smoke. The combustion of hydrocarbons that slip through the DOC and enter the DPF may cause damage to the DPF.
There are several causes for hydrocarbon slip, such as insufficient oxygen within the exhaust system to allow the hydrocarbons to combust in the DOC, an aged, damaged, or inefficient DOC, and a hydrocarbon injector that is leaking hydrocarbons or is injecting more hydrocarbons than anticipated. Systems to estimate the oxygen available for hydrocarbon combustion in an exhaust system and limit hydrocarbon injection accordingly have been developed, therefore, a need exists for a system and method to detect hydrocarbon slip through a DOC based upon the DOC being aged, damaged, or inefficient as well as hydrocarbon slip through a DOC based upon a hydrocarbon injector that is leaking or is injecting more hydrocarbons than anticipated.